Dumbbell



FIG. 1 is a front, right side, perspective view of a dumbbell showing our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof;

FIG. 7 is a bottom view thereof; and,

FIG. 8 is another perspective view shown in a usage condition.

The dashed broken lines in FIG. 8 represents environment and forms no part of the claimed design. 

CLAIM The ornamental design for a dumbbell, as shown and described. 